#define _CRT_SECURE_NO_WARNINGS 1


 //Definition for a binary tree node.
 struct TreeNode {
 int val;
      TreeNode *left;
      TreeNode *right;
      TreeNode() : val(0), left(nullptr), right(nullptr) {}
      TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
      TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
  };
 
class Solution {
public:
    int minDepth(TreeNode* root) {
        if (root == nullptr)
            return 0;
        if (root->left == nullptr && root->right == nullptr)
            return 1;
        if (root->left == nullptr)
            return minDepth(root->right) + 1;
        if (root->right == nullptr)
            return minDepth(root->left) + 1;
        int left = minDepth(root->left);
        int right = minDepth(root->right);
        return left < right ? left + 1 : right + 1;
    }

};